How to assign a default parameter to a function aside of map parameter in dart-CodePudding

Any idea how to assign a default parameter to a function aside of Map parameter in dart?

static Future functionName(
  bool isDone,
  [
    Map<String, String> params,
  ]
) async {
    ....
}

Note that if I put functionName([...],{bool isDone = false}) it doesn't work until I remove [...],

CodePudding user response：

If you want isDone to have a default value, that means it will need to become an optional parameter. Your function has an existing optional positional parameter (params), and Dart currently does not allow mixing optional positional parameters with optional named parameters. Therefore for isDone to be optional, it also must be positional. To avoid breaking existing callers, it should remain the first parameter:

static Future functionName([
  bool isDone = false,
  Map<String, String>? params, // Remove the `?` if you don't enable null-safety.
]) async {
    ....
}

and then you would call it the same way that you already do:

functionName(
  true,
  {
    'key1': value1,
    'key2': value2,
    ...
  },
);

The only difference between this and your existing code is that you now will be able to call your function as just functionName(). If you want callers to be able to call your function with params but not with isDone, then that would be a breaking change (you would need to update all callers) and would require reordering the parameters or changing the parameters to optional named parameters.

CodePudding user response：

A friend helped me with this and figured out that function args can take default values have to be given inside [] or {}, so this is how we pass it:

static Future functionName(
  [
    Map<String, String> params,
    bool isDone = false,
  ]
) async {
    ....
}

And call it like this:

functionName(
  {
    'key1': value1,
    'key2': value2,
    ...
  },
  true,
);